Many scientific instruments require a large number of electrical connections, for example to supply power to modules of the scientific instrument or to allow transmission or receipt of the measurement signals. Some of the electrical connections will carry high voltages (in some cases on the scale of kV). Other connections carry much smaller voltages, for example control or measurement signals of a few V or mV.
When connectors carrying high voltages come into close proximity with a connection to the ground potential (or connectors carrying much lower voltages) there is a risk of an arc or spark. The arc may be formed across an air gap if the breakdown voltage of the air gap is exceeded by the difference between the potential at the two regions. This type of arc or discharge can be hazardous, causing damage to the equipment and injury to the user. Therefore, a sufficient air gap should be maintained to prevent this type of leakage pathway to ground.
Commonly, to connect electrical connections to a scientific instrument the operator will separately connect each individual electrical lead from a bundle of electrical cables. The cables may then trail from each connector at the instrument during use, and may be prone to inadvertent contact or movement. This can result in reduction of the spacing between connectors or leads carrying different voltage, and so discharging events may occur. Furthermore, connection and disconnection of each electrical connection separately is time consuming and leaves room for error. If an unexpectedly high voltage is applied to an incorrect electrical connection at the scientific instrument, damage or hazard can occur.
Micro-discharging is also a particular problem in high voltage connectors. Micro-discharging occurs due to charges accumulating at insulating surfaces close to the high voltage lead. If the spacing between the charged surface and a region of lower potential is too small, a temporary pathway across the insulating surface may formed, thereby allowing for micro-discharging events. These events are observed as relatively small, brief fluctuations in the voltage passed through the connector. For example, when a 10 kV voltage is supplied to the connector, dips of around 1V over 10 ms may be observed due to micro-discharging. As such, micro-discharging cause instability in the voltage supplied through the electrical connection, which can be problematic for certain voltage-sensitive scientific instruments.
A method used to prevent micro-discharging is to provide a sufficient spacing between the electrical lead and regions provided at a lower or ground potential. A steep potential gradient across the surface of the insulator should be avoided. The spacing, d, required to prevent micro-discharging scales exponentially with the voltage difference, ΔV, between the two regions (in other words, d∝ekΔV). For example, when situated in air the required spacing between the high-voltage region and ground with an applied voltage of 5 kV must be greater than or equal to 24 mm, whereas the required spacing for an applied voltage of 10 kV must be greater than or equal to 290 mm. The set-up of scientific instruments and their electrical connections can be designed to maintain the required air gap between electrical components, but this becomes more complex and cumbersome where large voltages are required.
Electrical connection to a mass spectrometer can be especially complicated. Not only are a large number of electrical connections required, but a number of the connections must be provided at very high voltages (up to 10 kV). Mass spectrometers require a particularly stable voltage supply to the electrostatic analyser. Even small fluctuations in the supplied potential can disrupt the ion optics and reduce the resolution limit of the instrument. Furthermore, the apparatus is both delicate and of high value, and so avoiding damage due to incorrect configuration of the electrical connections is of paramount importance.
Accordingly, there is a need to provide a method and apparatus for electrical connection to a scientific instrument which reduces the likelihood of micro-discharging events whilst being more convenient and less prone to error. There is further a requirement to provide an electrical connector which reduces the likelihood of micro-discharging in order to maintain a stable applied potential.